Episodic Sedimentary Evolution of an Alluvial Fan (Huangshui Catchment, NE Tibetan Plateau)

Linman Gao,Jef Vandenberghe,Xianyan Wang,Shuangwen Yi,Martin Gibling,Huayu Lu

doi:10.3390/quat1020016

Linman Gao, Jef Vandenberghe + Show 4 more

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https://doi.org/10.3390/quat1020016

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Journal: Quaternary	Publication Date: Sep 3, 2018
Citations: 12	License type: CC BY 4.0

Affiliation: Nanjing University, Dalhousie University

Abstract

Alluvial-fan successions record changes in hydrological processes and environments that may reflect tectonic activity, climate conditions and changes, intrinsic geomorphic changes, or combinations of these factors. Here, we focus on the evolution of a stream-dominated fan in a tectonic depression of the Xining basin of China, laid down under a semi-arid climate in the northeastern Tibetan Plateau (NETP). The fan succession is composed of three facies associations, from bottom to top: (1) matrix to clast-supported, poorly sorted, planar cross-stratified to crudely stratified sheets of coarse-grained sediments; (2) horizontal laminated sand, laminated layers of reddish fine silt and yellow coarse silt with stacked mounds of sand; and (3) clay-rich deposits with incipient paleosols. The succession shows rapid sediment aggradation from high-energy to low-energy alluvial fans and finally to a floodplain. The dating results using optically stimulated luminescence (OSL) method show that a gravelly, high-energy fan was deposited during MIS 6, after which a low-energy fan, mainly composed of sand and silt, was deposited and finally covered by flood loam during the MIS 6–5 transition and the warmer last interglacial. Stacked sand mounds are interpreted from their sediment structure and grain-size distribution as shrub-coppice dunes in low-energy fan deposits. They may be considered as a response to the interaction of alluvial and aeolian processes in a semi-arid environment.

Highlights

Quaternary terrestrial sediments record information on climatic conditions and changes, environmental evolution, and tectonic events
The strata are subdivided into six units (Figure 2) and grouped into three facies associations from bottom to top: a high-energy alluvial fan, low-energy alluvial fan, and floodplain
Three facies associations are recognized in upward succession: (1) a high-energy association with matrix- to clast-supported, disorganized, and organized gravel sheets, interpreted as highly concentrated streamflow deposits; (2) a low-energy association with laminated sand and interbedded laminated silt and sand, with vertically stacked sand mounds and dispersed gravel lenses, interpreted as braided-stream and sheet-flood deposits; and (3) a floodplain association composed of massive silt with incipient palaeosols, interpreted as the result of settling from floodwaters and weak pedogenesis

Summary

Introduction

Quaternary terrestrial sediments record information on climatic conditions and changes, environmental evolution, and tectonic events. The intricacy of fluvial response, including aggradation/incision rhythms and terrace formation, to late Quaternary climate change, has been studied for several decades [16,18,19,20,21]. The interactions between fluvial and aeolian processes and their response to climate change in semi-arid areas have been reported elsewhere in China and around the world [22,23,24,25,26]

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